Memory storage units known as bit cells store information in the form of single bits. Static random access memory (SRAM) is a type of semiconductor memory that stores data in the form of bits using bistable circuitry without the need for refreshing. In a volatile memory such as SRAM, stored information therein is not retained after a power-down or power off event. In contrast, non-volatile memories store their contents after power is turned off and such contents are available for access upon subsequent power-on. Memory arrays include multiple bit cells arranged in rows and columns. Each bit cell in a memory array typically includes connections to a power supply voltage and to a reference voltage. Bit lines are used for accessing a bit cell, with a word line controlling connections to the bit lines. A word line may be coupled to the bit cells in a row of a memory array, with different word lines provided for different rows.
A failed bit cell may result in incorrect storage of data and unreliable reads/writes to/from the bit cell. Failure of bit cells in a memory array is a challenge for the data storage industry. The major failure mode encountered in practice is a random single bit (individual bit failure) as opposed to failure of an entire row (e.g., word line) or bit line.